(a) Field of the Invention
The present invention relates to a system and method for controlling a vehicle using an in-wheel system. More particularly, the present invention relates to a method for controlling a vehicle using an in-wheel system which can minimize a radius of rotation with turning stability by using Ackerman tendency steering principle.
(b) Description of the Related Art
An in-wheel system generally has an electric motor mounted within each wheel of a vehicle and directly controls driving of each wheel. The in-wheel system is normally used in a vehicle using an electric motor as a power source such as a hybrid vehicle, a fuel cell vehicle, and an electric vehicle.
In general, this type of steering apparatus is provided for controlling a direction of travel of a vehicle. The steering apparatus transfers power from a gear apparatus to front wheels of the vehicle and includes a tie rod and a knuckle arm for supporting a relational position between left and right wheels.
The steering apparatus generally follows an Ackerman tendency steering principle. An Ackerman geometry condition can be established between a rack stroke generated by steering angle and tire angle, and an Ackerman angle and an Ackerman rate can be defined as mentioned below under the Ackerman geometry condition.
The Ackerman angle can be defined as a tire angle of the outer wheel when the normal lines of the front wheel and the rear wheel pass through a center of pivot, and the Ackerman rate can be defined as the ratio (%) between a theoretical Ackerman angle and a real tire angle generated in actual driving. The Ackerman angle and the Ackerman rate may be calculated by a formula shown in FIG. 1.
It would be ideal if the Ackerman rate is 100%, but in actuality the Ackerman rate is designed to be 40-80% according to steering angle based on some limiting conditions with other link parts. If the Ackerman rate is not properly applied, some problems such as tire drag or degraded steering sensing may occur.
In the case of the conventional art, as shown in FIG. 1, a centrifugal force is applied to the vehicle when the vehicle is turned. A cornering force is applied to the tire of the vehicle and tire slip occurs to offset the centrifugal force. The Ackerman geometry condition cannot be satisfied when the tire slippage occurs since the center of pivot (O) moves to an upper position (O′) due to the tire slip. As a result tire drag occurs in the conventional art and steering sensing is degraded. Further, as shown in FIG. 2, the conventional art has a problem that the Ackerman rate falls when the vehicle is turned normally since the steering angle is quite small in normal turns.
On the other hand, a large outer wheel angle is more advantageous for minimizing a radius of rotation when the vehicle requires turning with a minimum radius of rotation. In this case, the steering angle should be larger so as to minimize the radius of rotation, and when the steering angle becomes larger, then the Ackerman rate increases as shown in FIG. 2.
However, according to the Ackerman rate formula shown in FIG. 1, the Ackerman rate has a large value when the inner wheel angle is greater than the outer wheel angle. As a result, in the conventional art, it is difficult to minimize a radius of rotation by maintaining turning stability, since the outer wheel angle should be smaller to increase the Ackerman rate and it is disadvantageous for minimizing the radius of rotation.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.